text: // Copyright 2014-2016, Google, Inc.
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //    http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  
  'use strict';
  
  const {google} = require('googleapis');
  const fs = require('fs');
  const path = require('path');
  
  /**
   * The JWT authorization is ideal for performing server-to-server
   * communication without asking for user consent.
   *
   * Suggested reading for Admin SDK users using service accounts:
   * https://developers.google.com/admin-sdk/directory/v1/guides/delegation
   *
   * See the defaultauth.js sample for an alternate way of fetching compute credentials.
   */
  
  let keys = {};
  const keyPath = path.join(__dirname, 'jwt.keys.json');
  if (fs.existsSync(keyPath)) {
    keys = require(keyPath);
  }
  
  // Create a new JWT client using the key file downloaded from the Google Developer Console
  const jwtClient = new google.auth.JWT({
    email: keys.client_email,
    key: keys.private_key,
    scopes: 'https://www.googleapis.com/auth/drive.readonly'
  });
  
  // Obtain a new drive client, making sure you pass along the auth client
  const drive = google.drive({
    version: 'v2',
    auth: jwtClient
  });
  
  // Make an authorized request to list Drive files.
  function runSample (callback) {
    drive.files.list((err, res) => {
      if (err) {
        throw err;
      }
      console.log(res.data);
      callback(res.data);
    });
  }
  
  if (module === require.main) {
    // Run `authorize` to obtain the right tokens for auth
    jwtClient.authorize(err => {
      if (err) {
        throw err;
      }
      // Now that we have credentials, run the sample
      runSample(() => { /* complete */ });
    });
  }
  
  // Exports for unit testing purposes
  module.exports = {
    runSample,
    client: jwtClient
  };
  